How to determine required screening area
How to determine required screening area
A separate calculation is required for each deck of a multiple deck screen, although the same formula is utilized for each calculation.
Screening Area = U = Square Feet
A x B x C x D x E x F x G x H x J
The succession of unknowns that must be established before using the formula is as follows:
Factor "U" - Undersize Amount in STPH of material feed to deck that is smaller than a specified aperture.
Predetermined rate of material STPH through a square foot of woven wire cloth with a specified opening when feed to deck contains 25% oversize (Factor "B") and 40% halfsize (Factor "C").
Actual % of material in feed to screen deck that is larger than a specified aperture. (Adjusts Factor "A" to suit conditions)
Actual % of material in feed to the screen deck that is one-half the size of a specified aperture. (Adjusts Factor "A" to suit conditions).
Applies for multiple deck screens. Total screening area is available for top deck separation. Time delay for material to pass top deck and 2nd or 3rd decks leaves less effective area available. This factor is expressed as a percentage of the top deck effective area.
Applies when water is sprayed on the material as it moves down the screening deck. Generally, about 5 to 7 GPM of water is used per STPH of solids fed to the screen. The volume of water required should be supplied so that a portion is combined with the solids into a feed box to prepare a slurry feed to the screen. The balance of water is added through a series of spray bars located over the screening deck.
Applies for weights other than 100 lbs. per cubic foot. If bulk density of one cubic foot of material weighs ± 100 lbs. cu.ft. Factor "F" =
lbs. per cu. ft.
100
Applies when open area of screening surface is less than the open area shown in the Factor "A" capacity chart. Factor "G" =
% open area of screen surface being used
% open area indicated in capacity chart
Applies when rectangular openings are used. Slotted or oblong openings will pass more material per square foot than square openings.
Applies when objective screening efficiency is less than 95%. Efficiency =
% of undersize in feed which actually passes
% of undersize in feed (should pass)
ALL FORMULAS ARE INTENDED TO BE USED ONLY AS A GUIDE.